Rek'Sai dominates early jungle pressure and must leverage this to disrupt Karthus's slower, full-clear tempo.
Prioritize early invades and river control to deny Karthus safe farming and delay his scaling power spikes.
Jungle Plan
Use fast clears and tunnel paths to repeatedly gank flashless or overextended lanes before Karthus hits level 6.
Invade Karthus early to force him off camps and deny his full clear tempo before his scaling powers come online.
Prioritize early dragon and Rift Herald control by using vision and lane priority to set up numbers advantages and force Karthus into unfavorable fights.
Danger windows
Rek'Sai is vulnerable during low-health clears and forced smite fights if lanes cannot move first.
Avoid isolated river fights where Karthus can kite with (Q) and slow with (W), especially before Rek'Sai's level 6.
Respect Karthus's scaling window post-level 6 and item spikes when his global damage and objective presence increase significantly.
Early game
Start with a three-camp clear into an immediate invade or counter-invade to punish Karthus's vulnerable early pathing.
Fight for first Scuttle when nearby lanes have priority to secure river control and deny vision for Karthus.
Avoid extended river fights if lanes lack priority to prevent getting collapsed on during low-health clears.
Power spikes
Rek'Sai's level 3 three-camp clear enables strong early invades and ganks; use this to snowball lanes.
Karthus's level 6 unlocks global damage with (R); avoid extended low-health fights across the map after this point.
Karthus's first AP item spike accelerates his clear speed and objective damage; use Rek'Sai's mobility to contest camps and objectives before this timing.
Win conditions
Convert early tunnel ganks and invades into sustained lane pressure and camp denial to delay Karthus's scaling.
Control river vision and secure early dragons and Rift Herald to force Karthus into reactive, unsafe plays.
Use Rek'Sai's mobility and knockup to create numbers advantages in skirmishes before Karthus can leverage his global damage.
Tip: For Rek'Sai vs Karthus, read overview, trading pattern, and danger windows first for a fast Jungle lane check.
